Interactive Web Mapping: Overview

Transcription

1 Interactive Web Mapping: Overview

2 Overview of how geospatial data is formatted requested supplied consumed by/for web technologies 2

3 Definitions Analysis exploring and modeling geospatial phenomena Mapping generating annotated pictures of geospatial information 3

4 Definitions Internet global network of computers communicating via TCP/IP World Wide Web Internet applications that communicate using HTTP protocol XML data formats optional: scriptable (JavaScript, CSS) clients 4

5 How The Web Works REpresentational State Transfer URL resource representation e.g. dataset in KML format HTTP request action on/with resource GET - return resource representation (i.e. state) POST/PUT - create new resource from representation UPDATE - change resource representation HTTP headers request status e.g. request succeeded, resource not found, etc. 5

6 URL Examples protocol: HTTP host: name: /~frew assumption: /~frew is Frew s home page protocol: HTTP host: name: /search query:?q=james+frew parameter: q values: james, frew assumption: /search is a service, not a static document 6

7 The Document Web browser HTTP server file system 7

8 The Document Web browser URL HTTP server file system 8

9 The Document Web browser URL HTTP server file name file system 9

10 The Document Web browser URL HTTP server file name content file system 10

11 The Document Web browser URL document HTTP server file name content file system 11

12 Now You Try It Start All Programs ScienceApps QGIS 3.2 OSGeo4W Shell C:\> H: H:\> cd ESM267 H:\ESM2962> python -m SimpleHTTPServer browse to URL: localhost:8000 in Python window: note how each link you click is a GET transac;on 12

13 Client could be on same machine, or in an internet cafe in Afghanistan 13

14 Client could be on same machine, or in an internet cafe in Afghanistan courtesy of Jorge Chen 14

15 Three-Tier Architecture Presentation: what you see Single user interface can access multiple applications E.g. web browser vs. e-commerce Application: what you do Single application can support multiple interfaces access multiple persistent stores Persistence: what you keep Single "repository" can support multiple applications e.g. database management system

16 The Service Web client application server database 16

17 The Service Web client URL application server database 17

18 The Service Web client URL application server query database 18

19 The Service Web client URL application server query results database 19

20 The Service Web client URL data application server query results database 20

21 GIS on the Service Web protocol Q: how ship GIS data? A: stick with HTTP well-supported (e.g. Apache, NGINX) scales (e.g. Google) gets through firewalls identifiers Q: how request GIS operations? A: stereotyped URLs Open Geospatial Consortium (OGC) W{M,F,C}S: Web {Map,Feature,Coverage} Service 21

22 Open Geospatial Consortium (OGC) Standards Product Access Standards Web Map Services (WMS) Web Feature Services (WFS) Web Coverage Services (WCS) Data and Representation Standards Geography Markup Language (GML) KML (introduced in 263, remember? ) 22

23 Comparison of OGC Services 23

24 OGC Web Map Services (WMS) client requests service metadata (GetCapabilities) Map Images (GetMap) Feature Information (GetFeatureInfo) server returns XML document describing service layers graphic layer rendering(s) for specified area of interest for specified time (optional) feature attributes at map image pixel location (various formats)

25 WMS GetCapabilities request Required SERVICE=WMS REQUEST=GetCapabilities Optional VERSION=version number in case you need to use a specific version of the protocol Example SERVICE=WMS&REQUEST=GETCAPABILITIES

26 WMS GetMap request Required REQUEST=GetMap LAYERS=layer1, SRS=EPSG:code spatial reference system BBOX=xmin,ymin,xmax,ymax WIDTH=#pixels HEIGHT=#pixels FORMAT=image_format gif, jpeg, png, etc. Example demo.boundlessgeo.com/ geoserver/opengeo/wms? SERVICE=WMS& VERSION=1.1.0& REQUEST=GetMap& LAYERS=opengeo:tracts& SRS=EPSG:4326& BBOX=-97.2,43.4,-89.4,49.4& WIDTH=768& HEIGHT=582& FORMAT=image/png

27 Geospatial Data Servers GeoServer open source self-contained: just download & run reads most geospatial data formats and databases shapefile, GeoTIFF, Arc GRID, PostGIS, serves as W{M,F,C}S can request a variety of formats 27

28 Geospatial Web Clients Download server simple, but not interactive Desktop application geospatial server map layer remote data Google Earth, QGIS, ArcMap, etc. thick client: lots of local capability installed / maintained independently of geospatial server Browser script geospatial server (portion of) web page JavaScript code remote data Leaflet, OpenLayers, etc. thin client: capability embedded in web page installed / updated whenever page is loaded

29 Additional References Web Architecture from 50,000 feet Sir Tim Explains It All For You MassGIS Geospatial Web Services Live WMS and WFS servers, plus tutorials How to link WMS layers to Google earth 29